FIX (KB3216755) – Windows Server 2016 Data Deduplication, data corruption warning!

Hello, in the last word from Gostev, he explained major data corruption warning for the enterprises who have already jumped the much improved Windows Server 2016 deduplication for production use. Last week, Veeam has started to receive multiple reports on corruptions of backup files hosted on Windows Server 2016 NTFS volumes with Data Deduplication feature enabled. Luckily, the issue was easy to spot due to the system event log event (rarely the case by the way, as most storage-level corruptions go undetected – which is why it is extremely important to have storage-level corruption guard enabled in the advanced backup job settings at least when you are trying out new things). Yesterday, Microsoft released the known issue (KB3216755) to fix for Data Deduplication in Windows Server 2016 in the most recent Windows update package! More information about Veeam Availability Suite 9.5 here and on Veeam portal.

Gostev’s recommendation (Veeam Software):

There are actually two separate issues, both leading to file corruption when using deduplication on very large files. One issue occurs when files grow to 2.2TB or larger, and another one causes loss of checksums for files with “smaller sizes” – this is the actual wording of the official note. As such, Gostev recommends assuming that all your existing backup can be damaged and perform an active full backup to a repository backed by a volume without deduplication feature enabled. Needless to say, since those of you who are affected already have a Windows Server 2016 based repository, he highly recommends that you use ReFS.

Solution (Microsoft KB):

Yesterday, Microsoft released the known issue: KB3216755 to fix for Data Deduplication in Windows Server 2016 in the most recent Windows update package. Microsoft recommends keeping your system up-to-date, based on the severity of any data corruption, we strongly recommend that everyone who is using Data Deduplication on Windows Server 2016 take this update.


Long-time users of Dedup on will note that we only officially support files with size up to 1 TB. While this is true, this is a “soft” support statement – we take your data integrity extremely seriously, and therefore will always address reported data corruptions. Our current defined support statement of 1 TB was chosen for two reasons: 1) for files larger than 1 TB, performance isn’t quite ‘up to snuff’ with our expectations, and 2) dynamic workloads with lots of writes may reach NTFS’ file fragmentation limits, causing the file to become read-only until the next optimization. In short, our 1 TB support statement is about preserving a high-quality experience for you. Your mileage may vary… in particular, many users have reported to us that backup workloads that use VHDs or VHD-like container files sized over 1 TB work extremely well with Dedup. This is because backup workloads are typically append-only workloads. We do however recommend that you make use of the new Backup usage type in Windows Server 2016 to ensure the best performance with backup workloads.Source: Microsoft Technet.


Need to deploy Veeam B&R 9.5 Update1? Follow this guide!

You can learn more about Veeam Backup & Replication 9.5 here.


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